DESCRIPTION (Adapted from application): Hepatitis C is an emerging infectious disease of major public health importance. Approximately 2% of the population of the USA and Europe are chronically infected with hepatitis C virus (HCV). Although major progress has been made in studies of the HCV genome and its encoded protein, basic aspects of the mechanisms of HCV pathogenesis are still poorly understood. One of the major difficulties has been the lack of an adequate tissue culture in which to study the interactions between HCV and hepatocytes, its natural host. Furthermore, the mechanisms of viral persistence and quasispecies evolution in HCV infected patients as well as the relationships between viral replication and disease progression remain to be determined. This application seeks to study the relationships between HCV replication and hepatocyte injury in a newly developed tissue culture system for human fetal hepatocytes (HFH) as well as in the human host. It is hypothesized that cell killing by apoptosis, preservation of permissive cells in which the virus persists and activation of cytokine signaling are events that occur in HCV infection and can be modified by the virus, the hepatocyte as its natural host or by interaction between virus and host cells. The application consists of 3 projects and 2 cores. Project 1 proposes to analyze HCV replication and the mechanisms of HCV-induced apoptosis in cultures transfected with full length HCV RNA or a 3'deleted virus used as control as well as in HFH cultures infected with patient sera. Project 2 will use cDNA microarrays to conduct a comprehensive analysis of gene expression in HFH transfected with full length and mutant HCV RNAs and investigate the effects of interferon on these cells. Project 3 will investigate the relationships between HCV replication, quasispecies evolution and hepatitis C disease progression in a population of Alaskan Native Americans (ANA cohort) from which serum, liver biopsies and clinical and epidemiological data have been collected.